Centrifugal switch



May 26, 1953 F. HElNzMANN CENTRIFUGAL swITcH Filed Feb. 28, 1951Patented May 26, 1953 OFFICE CENTRIFUGAL SWITCH Fritz Heinzmann,Albershausen, Kreis Goeppingen, Wurttemberg, Germany ApplicationFebruary 28, 1951, Serial No. 219,449 In Germany March 17, 1950 1 Claim.l

Induction motors are usually started by the aid of an auxiliary phase inwhich a current differing in phase from that of the working windings isproduced. When the starting process is at an end and a certain speed hasbeen attained, the auxiliary phase must be cut off automatically. Thisoperation is carried out by means of a Centrifugal switch. This switchcomprises a centrifugal speed governor and two contacts which are brokenand connected respectively by the governor. l

Cutting off the auxiliary phase must take plac instantaneously so thatthe spark may break olf and the contacts be protected against erosion.Astatic or unstable adjustment is therefore required for the centrifugalgovernor. Furthermore, switching oif the auxiliary phase must take placeat a precisely fixed speed allowing only a small tolerance. If the speedis too low at the moment when the auxiliary phase is switched o if, themotor will slow down and stop. If the speed is `too high, the auxiliarywindings will fuse. Small dimensions in length and diameter and absolutereliability in operation are further requirements such a switch has tomeet. Furthermore, the rotating masses must be as small as possible;otherwise there will arise, after some time of service, a rattling noisewhich is not permissible with regard to the use most of the motors inquestion are designed for. Besides meeting the beforementionedrequirements the centrifugal switch must also be simple and inexpensive.Repulsion motors start with a high starting torque. After the motor hasheen started. the armature winding is short-circuited by a centrifugalswitch, so that the motor continues working as an induction motor. Inthis case the centrifugal switch has to meet similar operatingconditions. The switch must be reliable, operating instantaneously at aprecisely xed speed. If the starting time is too long, the motor willheat up toc much and possibly get damaged,

The before-mentioned conditions are not or only partly met by thecentrifugal switches used at present for the purpose question. Thisdeficiency will be removed the present invention. According to thisinvention a centrifugal speed governor' having radially arrangedpressure springs-the design of such a governor in itself being knownismechanically and functionally combined with a conducting ring fixed tothe governor sleeve and sliding, while the motor is starting, on twostationary contacts. Besides this ina-in feature there are other newfeatures proving of value for the use in question.

Referring to the accompanying drawings: Fig. la is a perspective view.Fig. l is a longitudinal section, Fig. 2 a side view of such acentrifugal switch, while it is at rest, with closed contacts. Fig. 3 isa longitudinal section of the same centrifugal switch during normalworlr of the motor, the weights being swung out and the contactsseparated from each other. Figs. 4, 5, and 5 show a side view, alongitudinal section, and a top view of one of the weights I. Fig. 7shows a contact mechanism as it has hitherto been most usual. Fig, 8shouf's centrifugal force diagrams, the governor lift being drawn on theabscissa AB, and the centrifugal forces on the ordinate BC. X-X is therotation axis of the centrifugal governor. Figs. 9 and l0 show side viewand top view of the governor support.

The weights i are pivotally seated in the U- shaped part 2 by means ofpivots 3. Part 2 is iirmly connected with tube 4 fitted to the shaft.Parts f2 and 4 form together the governor support. The spring supports 5supporting the inner ends of pressure spings i5 are movably seated inthe weights I. The outer ends of these springs are supported by nuts Tscrewed on to bolts 8 firmly fixed to tube il. By means of arms il theweights i exert their pivoting action on governor sleeve lil. Aconducting ring il is firmly xed tc sleeve lil. While the motor isstarting, this ring,r slides on contacts i3 and lll fixed to stationarycontact bearer i2, thus conducting the current through these contacts.Conducting bars l5 are connected with the auxiliary phase.

l-litherto centrifugal governors having plate springs have sometimesbeen employedfor the purpose in question. Such plate springs are exposedto breaking if they are not treated carefully enough. The spring forcediagram varies according to but slight diierences in thickness of plate.such differences being unavoidable in manufacturing plate springs.Tension springs, which are also used, are particularly exposed tobreaking at their bent suspension loops. The spring force diagram showsrather considerable diiferencies, no uniform initial tension beingobtainable. Torsion springs acting on the link bolts, or axiallyarranged pressure springs are also used for the purpose in question.With such springs work consumed by friction is considerable, because thesprings transmit their full load on the lin Is. Hence it follows thatthe centrifugal switch operates at varying speeds owing tc the varyingconditions with regard to friction or lubrication. Plate springs ortension springs or torsion springs allow speed regulation only within anarrow range able for the purpose in question..

.and i4.

and by using conioiicated means. Pressure springs, however, are easilyadjustable, so that the characterstic and speed required for the purposein question is obtainable with all desired accuracy. Furthermore,pressure springs absolutely reliable in operation and resisting tofracture, however rudely they may be treated. Speed control within acomparatively *if e range is possible by simply adjusting the nuts l. sthe centrifugal force of the w lits i directly opposes the force of thesprings t friction is reduced to the minimum, so that the speed at whichthe switch required to operate always exactly the'sanie.

Fig. '7 shows a contact device as it has hitherto been most usual. Platespring I1 fixed `to oontact bearer h3 is stressed by the `governorsleeve while contacts i8 and i3 are inl closed `position, whereas it isreleased 'ii/'lien the weights move outwards, the contacts beingdisconnected Aat the same time. The lift of Contact spring il' isliniited. by plate vS shows the Centrifugal force diagram c-b--o t ofthe centrifugal speed governor having transverse sp `ings `theadjustment of the governor being astatic `it is -necessary for obtainingan instantaneo-1s operation. The centrifugal force dia-grani, which inthis case is nearly in accordance with the `diagram of -the transversesprings, intersects the axis of .the abscissa AB in the intersectionpoint with rotation axis. Sometimes unstahle adjustment i the governoris advisable, so that the centrifugal force diagram intersects the axisof the abscissa in a point that is still more f stent from being beyondthe rotation axis x Diagram.

a/-b--d respresents the force eidg-ram of the contact spring il. Thisspring must have acertain minimum power to ensure safe -disconncotion.of the contact i3. L the spring is too weak, the Contact does not breakoi', .and the motor will be damaged. a-c representing the Contact.spring force while the weights are in inward position, is longer thanb-d representing the contact sp ing torce while .the weights are inoutward position, so vthat o-b-e-f is the resultant centrifugal force ofthe governor combined with contactspring,T l?. Hence it folios/s Vthatthe governor -becomes static and thereby unserif'ice- Ir astatic orunstable adjustment of the governor combined with-contact spring I lshall be obtained, buildingin uncommonly heavy rfeghtsis necessary inorder t0 `increase the diierenoe between Contact spring force diagrama-b-c-d and centrifuga-l force diagram a-b-g-i. Such Weights `favour anoisy working of the governor and increase its construction dimensions.

The present invention .removes the beforeinentioned difoulty byproviding the .conducting ring H passing the current through contacts i3In .this case no additional spring power influencing the characteristicof the centrifugal governor in an unfavourable oanner., is required. Thediagram a-b-c--d is non-existent.

The weights l are made of sheet metal by noncutting shaping, thisworking process being most simple. They are provided with a radial hole2 I, an upright edge 22 having a rounded-off outside, and naps 23 havinga bent-in inside. The edge 22 and the flaps 23 serve to stiften theweights, and help to increase the governing power. The outside of theedge 22 is rounded off in order to obtain an accordingly smaller outsidediameter of the governor. The edge 22 engages in recesses 24 of theU-shaped part 2, which is also made of sheet metal by non-cuttingshaping. By this arrangement the construction length is reduced. Fixedin part 2 is a tube :l the bore of which deponds on the diameter of theshaft.

The governor support and the weights may also be cast, die-cast, orpressed.

The conducting ring may also be carried on the governor sleeve in ballbearing seat, so that it does not move when being in Contact with thecontacts, whereby wearing down the contacts due to friction .at theconducting will be avoided.

rShe new combination. described in lthis specification and theadditional foe-.tures of this invention provide for the construction ofa centrifugal switch that is reliable in service easily a retable.instantaneaousl;f switching, working with least possible noise,simplified and shortened in its design, whereby it 'meets therequirements such a deice is desired for, in a manner that has hithertobeen striven for by manifold vain efforts. As is apparent from thepresent specification, only part of these requirements would beachievedy if for example the centrifugal speedgovernor of the describedconstruction were coinbir d with a contact device .of anotherconstruction, or the described. contact device with another centrifugalspeed governor.

VI claim:

Centrifugal switch comprising .a support fitted to the shaft, twoweightspivotally connected with said support, pressure springs adaptedto oppose the outward movement of said weights and having their outerends in contact with nuts and their inner ends in contact with movablyseated spring supports, said nuts being screwed on to stay bolt screwsi'irnily'iixed to said support, said spring supports being movablylseated iii said weights, a sleeve slidingly seated on the shaft andmovably connected vith said Weights, a conducting `ring fixed to saidsleeve, a contact bearer fixed to the stationary centrifugal switchcasing, two contacts fixed to said contact bearer, conducting bars fixedto said contact `bearer and connected with said contacts.

FRITZ HEINZMANN.

References Cited in .the le of this patent UNITED STATES PATENTS NumberName Date 1,510,263 Defibaugh Sept. 30, 1924 1,552,589 White Sept. 8,1925 1,580,161 Persons Apr. 13, 1925 '2,318,313 House May 4, 1943

